The present invention relates to methods and compositions for increasing the viscosity of a fluid. More particularly, the present invention relates to divinyl sulfone crosslinking agents, viscosified treatment fluids, and methods of using these compositions in applications wherein viscosified treatment fluids may be used.
Many industrial applications require viscosified fluids or “viscosified treatment fluids.” For instance, the upstream energy industry uses viscosified treatment fluids in a variety of production and stimulation operations. For example, such fluids may be used as drilling fluids, fracturing fluids, and/or gravel packing fluids.
Viscosified treatment fluids that are used in subterranean operations generally are aqueous-based fluids that comprise gelling agents. These gelling agents may comprise biopolymers or synthetic polymers. Common gelling agents include, e.g., galactomannan gums, cellulosic polymers, and polysaccharides.
To increase the viscosity viscosified treatment fluid, often the gelling agent is crosslinked with the use of a crosslinking agent. Conventional crosslinking agents usually comprise a metal, transition metal, or metalloid, collectively referred to herein as “metal(s).” Examples include boron, aluminum, antimony, zirconium, magnesium, or titanium. Generally, the metal of a crosslinking agent interacts with at least two gelling agent molecules to form a crosslink between them, thereby forming a crosslinked gelling agent.
Many of the metal based crosslinking agents have drawbacks associated with their use. For instance, boron-containing crosslinking agents generally are limited to viscosified treatment fluids used in environments that have a pH of about 8 and above and a temperature below about 300° F. This pH requirement may preclude using salt water in a viscosified treatment fluid. Similarly, viscosified treatment fluids comprising gelling agents that are crosslinked with boron-containing crosslinking agents may suffer from thermal instability at certain elevated temperatures, like those frequently encountered in some subterranean operations. In addition, boron-containing crosslinking agents often react with additives commonly used with treatment fluids, e.g., glycols (such as ethylene or propylene glycol) or alcohols (such as methanol). To overcome this propensity, boron crosslinking agents typically are added in excess to treatment fluids, which may increase the environmental footprint and the costs associated with the treatment fluid. Similarly, titanium-based crosslinking agents have disadvantages. These include cost, delay in crosslinking, and a limited scope of gelling agents that may be crosslinked. Zirconium-based crosslinking agents also have drawbacks. One of the important drawbacks associated with zirconium-based crosslinking agents is their inability to crosslink xanthan, which is a commonly used gelling agent. Moreover, titanium- and zirconium-based crosslinks form permanent crosslinks that cannot be reversed, which may be undesirable. This quality is important when “breaking” (i.e., reducing the viscosity of) a viscosified treatment fluid comprising a crosslinked gelling agent that has been crosslinked with a titanium- or zirconium-based crosslinking agent because the breaking has to occur by breaking the gelling agent molecules rather than delinking the crosslinks, which can lead to formation fouling. Also, certain formation conditions and cationic species may be problematic for metal-based crosslinking agents.